Oxygen sensing in apple fruit

Oxygen plays a crucial role in sustaining plant life by acting as the final electron acceptor in the oxidative phosphorylation reactions. This allows for the efficient fixation of chemical energy in the form of ATP, the universal biological energy carrier. Metabolic processes requiring energy will convert ATP back to its precursor ADP and inorganic phosphate. To maintain their energy status, plants, like animals, require oxygen to recycle their ATP again. When oxygen drops below certain critical values, recycling becomes rate limiting, endangering the continuous supply of energy to sustain the energy demanding metabolism, eventually inducing stress. Depending on the severity, one discriminates between hypoxia (stress induced by low oxygen) and anoxia (stress induced by the complete absence of oxygen). During their sessile life, plants are mainly confronted with oxygen stress when exposed to flooding. Under these conditions oxygen deficiency has been shown to trigger a range of different responses ranging from rapid metabolic responses, like an increased glycolytic flux linked to the fermentation of pyruvate to ethanol, to structural morphological changes, like the formation of aerenchyma in maize or internodal elongation in rice (‘snorkelling’). Besides such imposed environmental stresses, oxygen limitation inherently occurs in bulky plant organs, like fleshy fruit, where diffusion is limiting the oxygen transport required to balance the high oxygen demand from an active metabolism. The aim of this PhD topic is to study the metabolic response of apple fruit as a response to hypoxic storage in relation to the turnover of the RAP2.12 oxygen sensor proteins or other members of the ERF-VII family transcription factors